1. Field of the Invention
The present invention relates to polymer mixtures of polyoxymethylene and modified polyacrylates, which can be thermoplastically processed.
2. Discussion of the Background
Controlling the properties of polymeric plastics by admixing other polymers with complementary properties is a technical concept that has been applied for a long time with impressive results (see: N. A. J. Platzer, Multicomponent Polymer Systems, Advances in Chem. Ser. 99, XI-XVIII, American Chemical Society, Washington, 1971; H. F. Mark, Encyclopedia of Polymer Science and Engineering, 2nd Ed., Vol. 12, pp. 399 to 461, J. Wiley & Sons, 1988). The blending frequently is intended to improve the impact strength properties of a plastic.
In other cases, the blending is carried out to replace relatively costly plastics by economical components.
In the case of polyoxymethylene (POM), it is not as likely to be deficiencies in the property profile as price considerations that justify blending with other plastics.
Precisely because of its favorable mechanical properties (hardness, rigidity, toughness down to low temperatures), and its resistance to solvents, polyoxymethylene has gained a firm position among structural materials (see: H. F. Mark et al., Encyclopedia of Polymer Science and Engineering, 2nd Ed , Vol. 1, pp. 42-61, J. Wiley, 1986; Winnacker-Kuchler Chemische Technologie, 4th Edition, Vol. 6; Org Technologie II, 4th Edition, Carl Hanser, Munich, 1982).
A number of examples of blends of polyoxymethylene with other plastics, which apparently pursue very diverse technological objectives, yet without the intention or achievement of true compatibility of the components are known. Thus, DE-A 27 09 037 describes a coating paste for projectile propellant charges that is obtained from a solution of POM, polymethyl methacrylate (PMMA), and paraformaldehyde in toluene (see: Chemical Abstracts, vol. 90, 206,733h). The property of POM of forming crystalline fibers has been utilized in various ways to produce fiber-reinforced plastics, including those based on PMMA (see: Chemical Abstracts, vol. 83, 148,276m; and Chemical Abstracts, vol. 87, 85,985u).
A high degree of attention has been directed to improving the impact strength of POM by blending with elastomers, for example acrylonitrile-grafted ethylenepropylene rubber (Chemicals Abstracts, vol. 99, 187,894c) or MMA-grafted polybutadiene (see: DE-A 34 41 547), or butadiene-MMA block copolymers DE-A 24 20 300) or butadiene-styrene or acrylonitrile-butadienestyrene graft copolymers (DE-A 19 31 392). Other impact strength modifications are acrylonitrile/styrene- or styrene-grafted polyoxymethylene (DE-A 26 59 357). Japanese Laid Open Patent Application 60-108,413 (Chemical Abstracts, vol. 104, 6,621r) recommends the production of high impact strength POM by polymerization of trioxane in the presence of an elastomer, for example an ethylenepropylene-2-hydroxyethyl methacrylate copolymer (see: also Chemical Abstracts, vol. 103, 19,692v). European Patent Application 115,373 recommends the addition of a multiphase crosslinked elastomeric copolymer to POM mixtures with a C.sub.10 -C.sub.30 -alkyl C.sub.2 -C.sub.7 -fatty acid ester and polymers such as caprolactam-caprolactone copolymers or polybutyl methacrylate, which are compatible with the fatty acid ester and inert toward POM. In German Patent Application P 38 05 052, compatible polymer mixtures of polyoxymethylene and 99.5 to 0.5 wt. % of a polymer that consists of 40 to 100 wt. % methyl acrylate or ethyl acrylate are described. Even in small proportions, the polyacrylate additives have a favorable effect on the processability of POM. However, there remains a need for POM mixtures which possess high solvent resistance and good mechanical properties and are thermoplastically processible.